EP1153308A4 - Partial discharge site location system for determining the position of faults in a high voltage cable - Google Patents
Partial discharge site location system for determining the position of faults in a high voltage cableInfo
- Publication number
- EP1153308A4 EP1153308A4 EP99964328A EP99964328A EP1153308A4 EP 1153308 A4 EP1153308 A4 EP 1153308A4 EP 99964328 A EP99964328 A EP 99964328A EP 99964328 A EP99964328 A EP 99964328A EP 1153308 A4 EP1153308 A4 EP 1153308A4
- Authority
- EP
- European Patent Office
- Prior art keywords
- pulse
- pulses
- buffer
- eleαrical
- samples
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/11—Locating faults in cables, transmission lines, or networks using pulse reflection methods
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
Definitions
- the invention relates to a system for determining the location of faults using multiple passes of pulse a ⁇ ivity on a condu ⁇ or being tested and averaging of dete ⁇ ed pulse a ⁇ ivity.
- the invention also relates to a system which performs partial discharge measurement and enhanced data acquisition using multiple passes of pulses and averaging without requiring the pulse triggering fun ⁇ ion of a digital oscilloscope.
- Partial discharge may occur along cables in electric power transmission and distribution systems when cable insulation breaks down.
- a cavity in cable insulation can cause partial discharges under normal operating conditions and test conditions when the cable is energized, that is, when high voltage signals are introduced into the cable.
- a partial discharge PD
- high frequency current and voltage pulses emanate from the site of the discharge, which is hereinafter referred to as a fault site.
- These current and voltage pulses can be useful as an indication of the presence of a fault (e.g., an insulation defe ⁇ ) for partial discharge site location and assessment.
- the type of cable fault that causes PD is non-reversible and damage to the cable progressively degrades the insulation until a catastrophic failure occurs.
- Partial discharge site location is a technique for determining the position of a fault within a high voltage (HV) cable by using dete ⁇ ion means at a near end of the cable to detect pulses which are generated by PD within the fault.
- the refle ⁇ ion of those pulses from the far end of the cable is also dete ⁇ ed at the near end.
- the time difference between the PD pulse and its refle ⁇ ed pulse is proportional with respe ⁇ to the distance of the fault site from the far end of the cable.
- An existing partial discharge measurement (PDM) system employs a relatively simple discharge site location system which allows a user to perform a single time-related capture of pulse activity on a sample cable being tested.
- a user can employ the graphic user interface and processing capability of the PDM system to zoom in on pulses and their reflections and to determine the position of a fault within the cable.
- This single time-related capture technique has some deficiencies when compared with other equipment such as a digitizing oscilloscope. Since the above-described technique is a single shot process, no averaging of the data occurs. Thus, the PDM system sensitivity is limited by the non-correlated noise on the system.
- a digitizing oscilloscope is advantageous in that it can average pulse a ⁇ ivity by digitizing the pulse a ⁇ ivity in short bursts based on its time-base setting in response to a triggering event created by the presence of a pulse.
- the PDM system is designed to operate on a pulse-by-pulse basis to identify individual pulse events rather than relying on a repetitive signal, as is typically used for PDSL measurement.
- the redesign would involve considerable effort and expense to include the triggering system of an oscilloscope, as well as a philosophical change to the operation of the PDM system.
- the PDM system would change from an essentially free-running system to a triggered system so that, rather than looking for events in terms of peak heights (i.e., the fa ⁇ or of interest), the system would detect events crossing a defined threshold. This presents problems for PDM because of a possibility that events will be overlooked for failure to meet the trigger criteria. Accordingly, a need exists for a PDM system which can perform pulse averaging for PDSL without triggering and other operations associated with oscilloscopes.
- a single digitization system which allows both PDSL and PDM.
- Software processing of the information generated by a PDSL system is enhanced to perform averaging fun ⁇ ions such as those provided by a digital oscilloscope, as well as provide automation of the PDSL measurement process.
- An enhanced PDSL system is implemented in accordance with the present invention to provide a combination of accuracy, tolerance to noise and ease of use to the PDSL process.
- the software processing of the enhanced PDSL system is adapted for use with conventional time domain refle ⁇ ometry (TDR) systems without a PD measurement capability to enhance fun ⁇ ionality in the same way.
- TDR time domain refle ⁇ ometry
- a PDSL system is provided to determine cable propagation velocity, as well as a method for using same.
- the PDSL system introduces a calibration pulse (i.e., a pulse of insufficient power to cause discharge at faults) into a cable to be tested, and data capture operations are performed to relate the time required for a pulse to travel the full length of a cable being tested to the length of that cable.
- a calibration pulse i.e., a pulse of insufficient power to cause discharge at faults
- a method for applying an excitation pulse to a conductor being tested and for obtaining a statistical sum of pulse a ⁇ ivity on the condu ⁇ or in response to the excitation pulse.
- the statistical sum is obtained from buffering whereby pulse propagation time, cable length traveled by pulses and buffer positions for storing data relating to the pulses are correlated such that pulse a ⁇ ivity including refle ⁇ ions and interference occurring in a condu ⁇ or being tested is represented in predi ⁇ able buffer positions.
- a method is provided for determining the location of fault sites in a condu ⁇ or.
- a PDSL system comprises a pulse discharge measurement (PDM) system and is programmed to store the data captured by the PDM system in a reference buffer corresponding in size to the propagation time of a pulse along the length of the condu ⁇ or. Samples of the captured pulses are scanned to locate the peaks of pulses above a sele ⁇ ed noise level. These pulses are stored into a temporary working buffer, along with a sele ⁇ ed number of samples, normalized and then added to the reference buffer.
- the reference buffer provides a statistical average of pulse activity. Primary or excitation pulses and their reflections, as well as transient interference pulses and radio frequency interference, are indicated at the beginning and the end of the reference buffer. Reflections of pulses from fault sites are represented in the remaining portion of the reference buffer. Fault site distances from the end of the cable can be determined due to the proportional dimension of the reference buffer with respe ⁇ to the length of the cable and cable propagation time.
- Fig. 1 illustrates the configuration of a condu ⁇ or and a PDSL system constru ⁇ ed in accordance with an embodiment of the present invention to locate faults in the condu ⁇ or;
- Fig. 2 illustrates pulses and refle ⁇ ed pulses analyzed using a PDSL system during length calibration in accordance with an . embodiment of the present invention
- Fig. 3 is a block diagram of a PDSL system constructed in accordance with an embodiment of the present invention.
- Fig. 4 illustrates waveforms in the PDSL system depi ⁇ ed in Fig. 3
- Fig. 5 illustrates the capture of data by the PDSL system in accordance with an embodiment of the present invention
- Fig. 6 is a flow chart depi ⁇ ing a sequence of operations for calibrating a PDSL system and for determining a distance scaling fa ⁇ or in accordance with an embodiment of the present invention
- Fig. 7 is a flow chart depicting a sequence of operations for data acquisition via a PDSL system in accordance with an embodiment of the present invention
- Fig. 8 depi ⁇ s a buffer constructed in accordance with an embodiment of the present invention
- Figs. 9 and 10 illustrate pulses dete ⁇ ed on a condu ⁇ or by a PDSL system and their representation in a reference buffer in accordance with an embodiment of the present invention.
- an exemplary ele ⁇ rical condu ⁇ or 10 is illustrated, which is hereinafter referred to as a cable for illustrative purposes. It is to be understood that the system and method of analyzing pulse a ⁇ ivity of the present invention can be used in a conne ⁇ ion with the testing of different media and different types of test signals.
- high voltage signals are used as test signals.
- a PDSL system 12 is conne ⁇ ed to the near end of the electrical condu ⁇ or 10 and is operable to introduce low voltage pulses (CP) therein for calibration.
- the PDSL system 12 also energizes the ele ⁇ rical condu ⁇ or 10 using high voltage AC or DC signals.
- the ele ⁇ rical condu ⁇ or 10 is therefore energized to the point where any faults 16 in the electrical condu ⁇ or 10 discharge and generate pulses that are measured by the PDSL system 12.
- a cable that is undergoing testing such as PDSL in a real environment is subje ⁇ to a number of forms of pulse a ⁇ ivity which all have an influence on the measurement of the position of the discharge source.
- a primary pulse is a discharge pulse from a fault site that has propagated down the cable toward the measuring end without being reflected.
- the path 18 of the PP is depi ⁇ ed in Fig. 1.
- the first refle ⁇ ion (FR) is the pulse PP' that has propagated along the cable to the far end 22 (i.e. the end that is furthest from the measuring point 24), has been reflected at the far end 22 and, consequently, has traveled toward the measuring end 24 (i.e., as exemplified by path 20).
- the time difference between the two pulses PP and FR is proportional to the distance X between the far end 22 of the cable and the fault site 18. This time difference is useful when performing PDSL measurements.
- the PDSL system 12 performs PDSL in an optimal manner by measuring the PP and the FR while reje ⁇ ing essentially all other forms of pulse a ⁇ ivity dete ⁇ ed along the cable.
- the FR pulse ordinarily has a lower magnitude than the PP because of the attenuation of the cable.
- the effe ⁇ is offset somewhat by the positive refle ⁇ ion coefficient at the far end 22 of the cable 10.
- the FR pulse is generally larger in magnitude than the primary pulse.
- the PDSL system 12 of the present invention preferably a measurement system which takes this difference in magnitude into account. Second and higher order reflections (SHOR), as illustrated in Fig.
- SHOR Second and higher order reflections
- Transient interference pulses can be coupled into the measurement system of the PDSL system 12 from the external environment via the cable 10 or the air, for example. These TTPs manifest themselves as pulses on either the near end 24 or the far end 22 of the cable 10.
- TTPs consist of a pulse with one or more refle ⁇ ions. The time spacing of these refle ⁇ ions is also proportional to the length of the cable and therefore the same as that for SHORs, as illustrated in Fig. 2.
- the TTPs are distinguishable from SHORs, however, in that they are not correlated to the PP and the FR.
- the TLPs occur randomly with respe ⁇ to the PP and the FR, as shown in phantom in Fig. 2 for illustrative purposes.
- Radio frequency interference can be coupled onto the PDSL system as a result of operating in an open, or an only partially shielded environment.
- spot frequencies or frequencies with sidebands can be coupled onto the cable 10. This has the effect of increasing the background noise level of the system, which may result in reflections being obscured, especially when the attenuation of the cable 10 is high.
- the RFI can be eliminated using averaging.
- the PDSL system 12 comprises a digital peak dete ⁇ ion measurement system 30 and means for generating high voltage signals 32.
- the PDSL system 12 is operable with an external high voltage power supply.
- a high voltage power supply which can be incorporated into or conne ⁇ ed to the PDSL system is, for example, any of the power supplies based on the 970 Series system controller available from Hipotronics, Inc., Brewster, New York.
- a block diagram of a digital partial discharge measurement (PDM) system 30 which implements digital peak dete ⁇ ion in the PDSL 12 and operates in accordance with the present invention is depi ⁇ ed in Fig. 3. Signal waveforms A, B and C at the outputs of various components in the PDM system 30 are illustrated in Fig.
- Applications for the PDM system 30 include, but are not limited to, testing and monitoring power cable, distribution and power transformers, medium and high voltage switch gear, power circuit breakers, gas insulated switch gear, bushings, shunt rea ⁇ ors, potential and current transformers, power fa ⁇ or corre ⁇ ion capacitors, line insulator produ ⁇ s, lightening arrestors, among other high voltage components and insulating materials of all types.
- a sample (e.g., an insulation system sample such as the cable 10) which is to undergo partial discharge dete ⁇ ion using the PDM system 30 is conne ⁇ ed to a coupling impedance 34.
- the PDM system 30 is preferably not steady-state and pulses are frequently superimposed on the high voltage waveform condu ⁇ ed across the sample 10 from a high voltage source 32.
- the waveform provided to the coupling impedance 34 is illustrated as waveform A.
- the magnitude of the pulse 36 superimposed on the high voltage waveform A has been exaggerated for illustrative purposes.
- the output of the coupling impedance 34 is depi ⁇ ed as waveform B in Fig. 3. Following processing by amplifier 36, the pulse can appear as the waveform C in Fig. 3.
- digital peak dete ⁇ ion is performed by a peak dete ⁇ ion circuit 40 comprising a digitizer 42, and peak dete ⁇ ion and processing logic 44.
- the output of the peak dete ⁇ ion logic 44 is passed to a buffer memory 46 and subsequently to a computer 48.
- the computer 48 is preferably conne ⁇ ed to a display device 50 and performs other processing and display fun ⁇ ions.
- the PDM system 30 preferably provides at least two basic modes of operation for use in different applications.
- the basic modes are: (1) general purpose measurement and pulse display; and (2) time-dependent pulse capture.
- a pulse capture and analysis mode using varying windows is also described in the aforementioned co-pending applications.
- the PDM system 30 When operating in general purpose measurement and display mode, the PDM system 30 most closely mimics the operation of a traditional instrument. This mode is optimized to provide the fastest possible update rate on the system display 50 to allow the PDM system 30 to mimic the chara ⁇ eristics of an analog cathode-ray oscilloscope, for example.
- individual pulses are captured in fixed windows (e.g., window 56), taking into account the positive and negative peak magnitudes.
- the pulses are each stored in a capture memory based on their position in the cycle of a clock signal 58, and the number of cycles that have elapsed since the last time the capture memory was read. Having the phase implicit in the position of a . pulse in the capture memory simplifies the process of writing the individual pulses onto the system display 50 by minimizing the calculation required. Where pulses occur so close together that they occupy a single phase position 56, the PDM system 30 records the highest pulse and indicates the highest pulse on the system display 50.
- This mode guarantees that the highest discharge magnitude pulse is measured, but does not guarantee to resolve all pulses under all situations. In other words, multiple pulses occurring in one window 56 yields one result, while a single pulse crossing two windows yields two results.
- This mode does, however, provide a fast update rate (e.g., typically 25 times per second) combined with an accurate discharge magnitude measurement.
- the display produced looks like that on an analog display, in that it is bipolar and can display the overshoot on a pulse (i.e., a pulse occurring concurrently with the tail of another pulse). This makes the PDM system 30 comfortable for a user used to traditional instruments.
- the pulse capture and analysis mode is preferred over the general operation mode when it is required to look at the statistics of discharge a ⁇ ivity. For example, when discharge finge rinting is to be performed, all of the pulses in a defined interval can captured via the pulse capture and analysis mode. Nonetheless, the general purpose mode is advantageous for capturing the overshoot of the pulses to provide a more realistic display.
- the second mode of operation is the simplest mode of operation.
- the PDM system 30 is triggered in this mode (i.e., using fixed time windows as shown in Fig. 5)
- the PDM system 30 fills up a pulse capture memory with successive samples taken from the digitizer 42.
- this mode no attempt is made to capture the peaks of the pulses. Accordingly, no measurement of discharge magnitude is made.
- the primary use of this mode is for fault location in cables. The position of pulses within the cable 10 can be found by measuring the time interval between a pulse and its refle ⁇ ion.
- the computer 50 in the digital discharge dete ⁇ ion PDM system 30 is preferably a personal computer, for example.
- the computer 48 is figured to allow flexible test recording and data exporting to different software programs such as WordTM and ExcelTM
- the computer 48 is programmed to provide a flexible analysis tool for digital partial discharge dete ⁇ ion.
- Pulse capture is achieved against phase or time coordinates. Different modes of operation are provided for full control over gating of pulses in both the vertical and horizontal axes.
- FPGA technology is preferably used for peak dete ⁇ ion and operations (i.e., peak dete ⁇ ion logic 44) in conjun ⁇ ion with the central processing unit board of the computer 48.
- Pulses from the amplifier 36 are provided to the FPGA peak dete ⁇ or 40 which comprises a digitizer 42 (hereinafter referred to as an analog-to-digital converter (ADC)).
- the ADC 42 is preferably a 10-bit ADC to provide 9-bit resolution a sign bit.
- the output of the ADC 42 is provided to a two-stage pipeline comprising an ADC buffer and a peak buffer.
- the values in these buffers represent two stages in a pipeline and are provided to a magnitude comparator.
- a state machine controller in the peak dete ⁇ ion logic 44 provides gate control to determine the time window widiin which peak dete ⁇ ion is performed. The state machine also controls the clocking of the pipeline and resetting of values in the pipeline.
- the propagation time of a pulse travelling the full length of the cable is related to the length of the cable 10, in accordance with the present invention.
- a calibration pulse is inje ⁇ ed into the near end 24 of the cable 10 (i.e., at the measuring point).
- the calibration pulse (CP) preferably does not energize the cable 10 sufficiently for discharge activity to occur at faults, should any faults exist in the cable.
- the time difference between the inje ⁇ ion of the CP and the first reflection thereof (CP') is measured.
- the factor to relate the time difference between a PP and its refle ⁇ ion (i.e., FR) to the distance of the fault site 16 from the far end 22 of the cable 10 is obtained from the time difference between the calibration pulse (CP) and its refle ⁇ ion (CP') from the far end 22 of the cable 10.
- the PDSL system 12 can be used to provide calibration pulses to the near end 24 of the cable 10 and to trigger the PDSL capture of the system. Since the PDSL capture in the PDM system 30 does not occupy a full cycle of the power source 32, the PDM 30 is operable to ensure that the PDSL capture has a calibration pulse in it. Thus, the PDM system 30 is advantageous in that is it configured to allow the starting phase of the PDSL capture to be set and the phase position to be known. An important aspe ⁇ of the calibration of the PDSL system 12 is that the pulse is visible above the noise.
- the PDSL system 12 runs in the general measurement and pulse display mode, using the amplifier 36 to measure the background noise level of the system. The level is recorded, as indicated in block 60 in Fig. 6.
- the PDSL system 12 is programmable to commence calibration after the computer 48 has determined that a CP is introduced with a peak height of at least 50% greater than the recorded background noise level (block 62).
- the PDSL system 12 then preferably switches to the time- dependent pulse capture mode (hereinafter referred to as the PDSL mode) and triggers a series of captures (block 66).
- the data from multiple captures is combined as described below in connection with Fig. 6.
- the PDSL system 12 is programmed via the peak detection logic 44 to establish a primary reference buffer in the buffer memory 46) and to clear the primary reference buffer (block 68).
- PDSL measurement is commenced in the PDSL mode. Accordingly, data is captured into a second buffer in the buffer memory 46 (blocks 70 and 72). The data represents a time-based series of data points that provide ADC output at a particular instant.
- the PDSL system 12 searches the data in the secondary buffer until the peak of the calibration pulse is located, which is the highest value point recorded in the secondary buffer (block 74).
- the data in the secondary buffer is shifted until this peak value is stored at a predetermined position or register in the buffer (e.g., 10% into the buffer), as indicated in block 76. This eliminates problems due to jitter or synchronization drift by repositioning the peak to a known point.
- the data in the secondary buffer is added to that in the primary buffer (block 78).
- the process is repeated a number of times (e.g., between 50 and 100 times) to ensure that all non- correlated noise sources in the pulse stream (e.g., TTPs or RFI) are eliminated.
- the CP, its reflection CP', as well as TTPs and SHORs occur at similar time intervals t corresponding to the length / of the cable 10.
- the PDSL system 12 searches for the zero point of the CP in the secondary buffer and notes the CP position (block 80).
- the CP in Fig. 2 is illustrated as the first pulse ⁇ [A].
- the PDSL system 12 subsequently scans the secondary buffer for the CP refle ⁇ ion CP', assuming the refle ⁇ ion CP' is the second highest pulse (i.e., negle ⁇ ing the first highest pulse CP).
- the PDSL system 12 determines the zero point of the reflection CP' and the corresponding position of the zero value in the secondary buffer (block 82).
- the refle ⁇ ion CP' is illustrated in Fig. 2 as the second pulse ⁇ [B].
- the time difference between the CP and its reflection CP' is calculated (block 84), and a distance scaling factor is calculated from that time difference (block 86).
- the distance scaling factor can be l/t where the length / of the cable is known and the time difference is calculated.
- the distance scaling factor l/t is also equivalent to (/ x/ /n wherein /is the sampling frequency in the PDSL mode and n is the number of samples taken between pulses ⁇ [A] and ⁇ [B].
- the automatic calibration described in conne ⁇ ion with Fig. 6 need not be used to scale measurements if the cable propagation velocity is known.
- the PDSL system 12 is prepared to perform data acquisition and processing operations, which are described below in conne ⁇ ion with Figs. 7 and 8.
- the PDSL system 12 preferably captures data over a predefined number of acquisitions, set by the user or some suitable default setting.
- the amount of data that is gathered is a compromise between obtaining a sufficient amount of data to ensure that the full length of the condu ⁇ or 10 is measured, and avoiding the capture of an excessive amount of data and increased processing time.
- the computer can determine the amount of data based on the amount of memory left after the PP is dete ⁇ ed.
- the user can override the computer-determined amount if the user can estimate how much data is necessary, based on experience of the transit time or propagation speed of a particular type of condu ⁇ or or cable.
- the PDM system 30 can capture 0.25 Megabytes (MB) of information on each capture. Since, at a line frequency of 60 Hz, an whole entire power mains cycle may not be covered, it is necessary for the PDSL system 12 to know where on the mains cycle the data capture process is to start to ensure digitizing of valid discharge pulses. The starting point can be determined from the pulse information gathered while operating in the pulse display mode.
- MB Megabytes
- a high voltage signal is applied to the cable 10 which is sufficient for the cable 10 to discharge at any fault sites 16 therein (block 90 of Fig. 7).
- This high voltage energization can be generated, for example, using the /40982
- aforementioned 970 controller connected to, or incorporated in, the PDSL system 12. If the PDSL system 12 is using a 970 controller or similar device, there are at least two possibilities for applying voltage. First, a voltage level defined by the user or the PDSL system 12 can raise the voltage until a level of a ⁇ ivity defined by the user is achieved. Once a voltage is achieved whereby the sample discharge occurs, the voltage is preferably held until testing is completed.
- the starting point for digitization is determined (block 92).
- the starting position can be determined automatically if the discharge activity is visible over the background noise. It is to be understood that only the primary pulses (PPs) need to be visible.
- the user can indicate the starting position of the data capture sequence. For example, the user can set the starting position by observing the position of discharge a ⁇ ivity on the normal phase-related discharge display and choosing an appropriate value.
- the PDSL system 12 commences the data acquisition process (block 94). Data acquisition preferably involves a defined number of capture phases, the number of which can be set by the user. The higher the number of captures, the more statistically relevant the captured data is.
- the PDSL system 12 establishes a reference buffer 93 for the final gathered data which is illustrated in Fig. 8.
- the reference buffer 93 is sized according to the time difference between a calibration pulse and its refle ⁇ ion as measured during the calibration phase (Fig. 6).
- the use of the distance scaling fa ⁇ or determined during calibration ensures that the data buffer 93 corresponds to the length of the cable 10, in addition to small guard bands 97 and 99 of registers 95 added onto each end of the buffer 93.
- the contents of this reference buffer are set to zero, as indicated in block 96 of Fig. 7. For each of the data captures, the PDSL system 12 performs a sequence of operations.
- the PDSL system 12 After the PDSL system 12 commences the capture mode, as indicated in the decision block 98, the PDSL system 12 stores output values from the digitizer 42 (e.g., 10-bit representations of a waveform processed via an analog- to-digital converter) and continues to store values until 256K samples have been captured in the buffer memory 46 (block 100).
- the data from the PDSL capture is transferred into a working buffer in the buffer memory 46 (block 102).
- the system scans along the working buffer until it finds a pulse that exceeds the noise floor of the system (block 104).
- the PDSL system 12 locates the peak of that pulse. Once the peak has been found, the corresponding pulse is copied into a temporary buffer, along with a number of samples following the pulse (block 106).
- the number of the samples following the pulse corresponds to the size of the reference buffer and therefore the length of the cable.
- the entries in the temporary buffer are normalized to make the magnitude of the first pulse unity (block 108).
- the entries in the temporary buffer are added to the corresponding entries in the reference buffer (block 110).
- the data in the working buffer continues to be scanned and processed as described with reference to blocks 104, 106, 108, 110 until the entire working buffer is scanned (block 112).
- the reference buffer holds a sequence of data that represents the activity within the length of the cable.
- the reference buffer e.g., buffer 93 in Fig. 8
- the contents of the reference buffer represent a statistical average of the history of pulses over the time that elapsed while the pulses traveled the full length of the cable 10.
- a number of pulses A, B, C and D traveling along the cable 24 and measured by the PDSL system 12 at the measuring end 24 are depi ⁇ ed in Fig. 9.
- the pulses A, B, C and D are also depicted individually in Fig. 10, along with the history of the pulses 120 as represented in the reference buffer.
- the pulse B occurred at a time interval corresponding to the distance d on the cable, as depi ⁇ ed in Fig. 1.
- the pulses C and D each occurred at a time interval corresponding to / or the length of the table.
- the data detected at the near end or measuring point 24 of the cable 10 is depi ⁇ ed on the left of the raw data shown in Figs. 9.
- the contents of the reference buffer provide a plot of a ⁇ ivity along the length of the cable, as indicated at 120 in Fig. 10.
- the contents in the reference buffer corresponding to data at the measuring end 24 of the cable 10 essentially always comprises a pulse 122 which is the statistical sum of all of the pulses (e.g., pulses A, B, C and D) recorded during the data acquisition phase.
- the shaded area 124 in Fig. 10 represents the environment external to the cable, while the unshaded area corresponds to a ⁇ ivity in the cable 10.
- SHORs appear on the final result 120 in the reference buffer as a contribution to the pulse 122 at the start of the reference buffer and a corresponding pulse 128 at the far end of the buffer. This is so because, as stated previously, SHORs are spaced in accordance with the time corresponding to propagation of a pulse along the length of the cable. SHORs are therefore spaced apart or separated in time by this same amount. TTPs appear in the same way as they manifest on either one end 22 of the cable 10 or the other end 24.
- the effe ⁇ of SHORs and TIPs therefore is to accentuate the height of the pulse 122 at the start of the reference buffer and to produce a pulse 128 on the end of the buffer, thereby indicating the start and the finish points of the cable 10, respe ⁇ ively.
- RFI which does not correlate to the pulse a ⁇ ivity on the sample, is averaged over the length of the cable for a large number of captures, RFI is seen as an offset of the data in the reference buffer.
- the data of interest to most users are the PPs and FRs.
- the PPs e.g., pulse A in Figs. 9 and 10.
- the FRs e.g., pulse B
- pulses differ from the interferences and other refle ⁇ ions in that they are not spaced from the PP by the length of the cable, but rather by some lesser amount d.
- the effect of the PPs and FRs is to place pulses (e.g., pulse E in Fig. 10) inside the cable and not just on the ends as with SHORs and T Ps.
- data corresponding to FRs is contained somewhere in the reference buffer other than at the ends of the buffer.
- the FRs indicate fault sites 16. The location of the faults within the cable 10 therefore are indicated. Since the reference buffer length corresponds to the time elapsing as a pulse propagates along the length / of the cable, the time difference between the left side of the reference buffer and the pulse E indicates the distance d from the near end 24 of the cable or the distance x from the far end 22 of the cable. If no pulses are indicated between the ends of the buffer, a user can infer that a problem is close to the ends 22 and 24 of the cable 10, in the termination system at the far end 22 or external to the cable 10.
- the PDSL system 12 If the PDSL system 12 is operating with a 970 system controller, the user needs only enter the voltage at which the cable is to be tested, the number of capture cycles to be performed and either the length of the cable or its velocity of propagation. These parameters can be embedded in a test specification loaded from a file into the PDSL system 12. Once the PDSL system 12 has the required information, a test can be performed by pressing a button and waiting for the data to be produced. Thus, no intervention by the user is required. If the number of captures is sufficient to average out the non-correlated noise on PDSL system 12, the PDSL system can automatically locate the position of multiple faults within the cable 10, allowing the system to be used by unskilled operators with minimal training.
- the relative frequency of occurrence of the pulses is different and therefore the heights of the corresponding averaged pulses are different. Because the data are normalized based on the height of the primary pulse, there is no effect on the height of the first reflection pulses seen on the trace of the PDSL system display 50 as a result of differences in discharge magnitude.
- the height of pulses within the cable 10 are dependent on two factors, that is, the relative frequency of occurrences and the attenuation of the cable.
- the effe ⁇ of cable attenuation is proportional to the distance of the fault from the far end of the cable.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Testing Relating To Insulation (AREA)
- Locating Faults (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US225305 | 1999-01-05 | ||
US09/225,305 US6161077A (en) | 1999-01-05 | 1999-01-05 | Partial discharge site location system for determining the position of faults in a high voltage cable |
PCT/US1999/031032 WO2000040982A1 (en) | 1999-01-05 | 1999-12-29 | Partial discharge site location system for determining the position of faults in a high voltage cable |
Publications (3)
Publication Number | Publication Date |
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EP1153308A1 EP1153308A1 (en) | 2001-11-14 |
EP1153308A4 true EP1153308A4 (en) | 2003-06-11 |
EP1153308B1 EP1153308B1 (en) | 2005-11-23 |
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ID=22844366
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP99964328A Expired - Lifetime EP1153308B1 (en) | 1999-01-05 | 1999-12-29 | Partial discharge site location system for determining the position of faults in a high voltage cable |
Country Status (7)
Country | Link |
---|---|
US (1) | US6161077A (en) |
EP (1) | EP1153308B1 (en) |
CN (1) | CN1122852C (en) |
AU (1) | AU2059700A (en) |
DE (1) | DE69928571T2 (en) |
HK (1) | HK1043404B (en) |
WO (1) | WO2000040982A1 (en) |
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- 1999-12-29 AU AU20597/00A patent/AU2059700A/en not_active Abandoned
- 1999-12-29 EP EP99964328A patent/EP1153308B1/en not_active Expired - Lifetime
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Also Published As
Publication number | Publication date |
---|---|
CN1122852C (en) | 2003-10-01 |
CN1332853A (en) | 2002-01-23 |
HK1043404B (en) | 2004-07-02 |
DE69928571T2 (en) | 2006-07-27 |
EP1153308B1 (en) | 2005-11-23 |
US6161077A (en) | 2000-12-12 |
DE69928571D1 (en) | 2005-12-29 |
WO2000040982A1 (en) | 2000-07-13 |
AU2059700A (en) | 2000-07-24 |
EP1153308A1 (en) | 2001-11-14 |
HK1043404A1 (en) | 2002-09-13 |
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